Sealing device and production method thereof

ABSTRACT

A sealing device is provided which is capable of reducing its sliding resistance. In a sealing device  1  which is fitted into an annular groove formed in one of a housing with a shaft hole and a shaft inserted into said shaft hole and serves to seal an annular gap between these two members, and which includes a seal ring  2  made of a resin that is in sliding contact with the other of the two members, and an elastic ring  3  that is fitted between the seal ring  2  and the annular groove, the seal ring has a plurality of concave portions  22  formed on its sliding surface  20  which is in sliding contact with the other member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 U.S. National Stage of InternationalApplication No. PCT/JP2007/074145, filed Dec. 14, 2007. This applicationclaims the benefit of Japanese Patent Application No. JP 2006-336693,filed Dec. 14, 2006. The disclosures of the above applications areexpressly incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a sealing device used for a hydrauliccylinder or the like as well as to a production method of the sealingdevice.

BACKGROUND ART

In sealing devices used for hydraulic cylinders that are adapted to beused as driving means for construction machinery, there have beenproposed a variety of types of sealing devices in order to improve thelubrication property of sliding surfaces (see under-mentioned individualpatent documents).

For example, in a patent document 1, a sealing device is proposed whichis constructed of a seal ring made of PTFE (polytetrafluoroethyleneresin) and a thrust ring made of a rubbery elastic material is proposed.Although this sealing device is intended to reduce sliding resistance bythe use of PTFE for the seal ring which slides with respect to acounterpart member, it is inferior, in pressure resisting abilityagainst hydraulic pressure, to those made of nylon (polyamide typeresin), so it would sometimes be damaged or broken upon application ofhigh pressure while giving rise to a phenomenon of protrusion. Inaddition, a spiral groove formed on a sliding surface of the seal ringacts to place a pressure side and a non-pressure side in communicationwith each other to form an oil leakage passage, as a result of whichthere is a problem of low sealing performance.

In addition, in a patent document 2, there is proposed a sealing devicewhich is intended to improve the lubrication property by providing aplurality of annular protrusions on a sliding surface of a seal ring,which serve to retain lubricant. However, there is the followingproblem. That is, even if a flaw or the like is generated in eachannular protrusion at one place thereof, lubrication grooves betweenadjacent ones of the individual annular protrusions are placed incommunication with each other, so that a leakage passage leading from apressure side up to a non-pressure side is liable to be formed, thuseasily reducing the sealing performance. In another words, it can besaid that a safety factor with respect to the sealing performance islow.

Moreover, in a patent document 3, there is proposed a sealing devicewhich is intended to improve the lubrication property by providing aplurality of holes which serve to connect between an inner peripheralsurface and an outer peripheral surface of a low friction ring, butthere is a problem that the strength of the low friction ring itself isdecreased due to the provision of the holes. In addition, there is alsoanother problem that upon application of high pressure, an elastic sealring (a back ring made of rubber) is caused to protrude into the holesin the inner peripheral surface of the low friction ring, thus resultingin its damage.

Here, reference will be made to a sealing device that is proposed in apatent document 4, while referring to FIG. 12. FIG. 12 is a schematiccross sectional view of the sealing device according to the prior art.

A sealing device 100 serves to seal up an annular gap between an innerperipheral surface of a hydraulic cylinder 400 and an outer peripheralsurface of a piston 500, and it is fitted into an annular groove 600formed on the outer peripheral surface of the piston 500. The sealingdevice 100 comprises a seal ring 200 made of nylon that is in slidingcontact with the inner peripheral surface of the hydraulic cylinder 400,and an elastic ring 300 that is fitted between the seal ring 200 and agroove bottom of an annular groove 600 for pushing the seal ring 200against the inner peripheral surface of the hydraulic cylinder 400.

This sealing device 100 has an annular oil groove 700 which is formed onan outer peripheral surface of the seal ring 200, i.e., a slidingsurface thereof in sliding contact with the inner peripheral surface ofthe hydraulic cylinder 400, along a circumferential direction thereof.This oil groove 700 functions as a pressure chamber due to thegeneration of accumulated pressure caused by the pressure of accumulatedfluid to be sealed, whereby it serves to lubricate sliding portions andat the same time reduce an expanding force acting on the seal ring, thusmaking it possible to achieve a reduction in the sliding resistance ofthe seal ring.

However, when flaws or the like are generated in a pair of annularprotrusions, respectively, which form opposite side walls of the oilgroove 700, a leakage passage for the fluid to be sealed might beformed, thereby giving rise to a fear that the sealing performance ofthe seal ring 200 might be easily decreased. In addition, in order forthe oil groove 700 to exhibit the function of the pressure chamber to asatisfactory extent, a prescribed sliding distance is required, andhence there is a possibility that an expected effect might not beachieved in an initial stage of operation.

Further, to solve these problems, there is proposed a method in which asliding surface of a seal ring is processed by means of shot processingor the like so as to roughen the surface, thereby providing the surfacewith minute irregularities. However, there is the following problem.That is, as shown in FIG. 13, those portions lying between adjacentconcave portions become pointed protrusions, so high surface pressurewill be generated at these protrusions, whereby the minuteirregularities will be worn out in a relatively early time. Here, notethat FIG. 13 is a schematic cross sectional view of the irregularitiesformed by means of shot processing.

In addition, in case where nylon is used as a material for the pistonseal, the pressure resisting ability is more excellent but the slidingresistance be comes higher, in comparison with the case of using PTFE,so there is a problem that when a hydraulic cylinder is operated, aso-called stick-slip phenomenon will occur, thus ma king it easy togenerate vibration.

Moreover, as a high pressure piston seal, there has also been known asealing device which comprises a seal ring made of PTFE, back-up ringsmade of nylon arranged at opposite sides of the seal ring, and a biasingring for biasing these rings (for example, a patent document 8).However, this sealing device is composed of the four members, and hencehas a problem in that it is poor from a cost point of view.

-   Patent Document 1: Japanese utility model application laid-open No.    S60-101265-   Patent Document 2: Japanese patent application laid-open No.    H09-250640-   Patent Document 3: Japanese utility model application laid-open No.    S58-16459-   Patent Document 4: Japanese patent application laid-open No.    H10-213231-   Patent Document 5: Japanese patent No. 3114874-   Patent Document 6: Japanese utility model application laid-open No.    H04-136364-   Patent Document 7: Japanese utility model application laid-open No.    H04-129969-   Patent Document 8: Japanese utility model application laid-open No.    S59-180056

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present invention has been made to solve the problems of the priorart as referred to above, and has for its object to provide a sealingdevice which is intended to be capable of reducing its slidingresistance. In addition, another object of the present invention is toprovide a sealing device which can be produced at low cost whilemaintaining the function of a conventional sealing device.

Means for Solving the Problems

In order to achieve the above objects, a sealing device according to thepresent invention which is fitted into an annular groove formed in oneof a housing with a shaft hole and a shaft inserted into the shaft holeand serves to seal an annular gap between these two members, and whichincludes a seal ring made of a resin that is in sliding contact with theother of said two members, and an elastic ring that is fitted betweensaid seal ring and said annular groove, is characterized in that saidseal ring has a plurality of concave portions formed on its slidingsurface which is in sliding contact with the other member.

With this arrangement, a part of fluid to be sealed, which has leakedout from a region to be sealed to the sliding surface, is held orretained in the plurality of concave portions, respectively, formed onthe sliding surface, whereby the state of lubrication of the slidingsurface on the seal ring due to a lubricating film formed of the fluidto be sealed becomes excellent. In addition, a chamber, which is definedby the concave portions and a surface of the other member, functions asa pressure chamber, so that the contact pressure of the seal ring withrespect to the other member is reduced by the pressure of the fluid tobe sealed that is accumulated in the chamber, thus making it possible toreduce the sliding resistance thereof.

Said seal ring may preferably has convex portions which are formed so asto enclose said concave portions, respectively, and which rise from saidsliding surface and at the same time have initial sliding surfaces,respectively.

With such an arrangement, in the initial time of operation until thefluid to be sealed has accumulated in the concave portions, only theinitial sliding surfaces of the convex portions rising around theconcave portions, respectively, become in sliding contact with the othermember, so the contact areas of the seal ring with the other memberbecomes small, thus making it possible to reduce the sliding resistance.Accordingly, the sliding resistance until the formation of a stablelubricating film can be reduced, and the generation of stick-slip can besuppressed.

Further, the fluid to be sealed enters gaps which are formed between theadjacent individual convex portions, whereby the fluid to be sealed canbe positively introduced into the sliding surface, and the accumulationof the fluid to be sealed in the concave portions can be made faster,and at the same time the state of lubrication of the sliding surface atthe time of system starting (initial operation stage) can be madeexcellent.

In addition, at the time when the convex portions are worn out due tothe sliding contact thereof with the other member, a sufficient amountof fluid to be sealed is accumulated in the concave portions and at thesame time a sufficient lubricating film is formed on the slidingsurface, thereby making it possible to maintain an excellent lubricationstate.

Said concave portions may preferably be formed by irradiating laser tosaid sliding surface, and said convex portions may be formed by risingof a material around opening portions of said concave portions,respectively, which is melted by the irradiation of the laser.

Thus, the concave portions and the convex portions can be formed in asimple and easy manner.

Said seal ring may preferably be made of a resin material of which abase polymer is a thermoplastic resin.

Thus, the pressure resisting ability or property can be made higher, soa stable seal performance can be exhibited. In addition, in case wherethe concave portions are formed by means of laser processing, the convexportions can be easily formed of a part of the material melted due tothe heat of the laser.

Moreover, in order to achieve the above-mentioned objects, a productionmethod of a sealing device according to the present invention is amethod for producing the above-mentioned sealing device, and ischaracterized by comprising forming said concave portions by irradiatinglaser to said sliding surface, and forming said convex portions byrising of a material around opening portions of said concave portions,respectively, which is melted by the irradiation of the laser.

With this method, the concave portions and the convex portions can beformed in a simple and easy manner.

Said seal ring may preferably be made of a resin material of which abase polymer is a thermoplastic resin.

Thus, the pressure resisting ability or property can be enhanced, so astable seal performance can be exhibited. Also, in case where theconcave portions are formed by means of laser processing, it is possibleto form the convex portions by a part of the material melted due to theheat of the laser in an easy manner.

Effects of the Invention

As described in the foregoing, according to the present invention, it ispossible to achieve a reduction in the sliding resistance. In addition,a general-purpose resin can be used for a high pressure piston sealcomprising four members because of the improvement in the slidingproperty of the seal ring, and hence the cost of materials can bereduced, thus making it possible to produce the piston seal at low cost.Further, in a sealing device comprising two members of a seal ring madeof a resin and an elastic ring, if PTFE is applied which is usedgenerally and widely as a sliding material, the sliding property of thesealing device can be further improved, and if a general-purpose resinis applied, the cost of materials can be reduced, so a low costproduction of the sealing device becomes possible. In other words, thepresent application is not limited to such combined sealing devices, butcan achieve the reduction of the sliding resistance with respect toresin-made sliding members (for example, seal rings, wear rings, etc.)in a simple manner.

More specifically, the present invention is able to achieve, in asealing device provided with a sliding surface, an improvement in thesliding property of the sealing device by devising the shape of thesliding surface without regard to the characteristic or property ofmaterials used. Accordingly, the range of selection of materials can beextended (i.e., it becomes possible to adopt inexpensive materialshaving not so high sliding properties), whereby the reduction in thecost of materials can be made. In addition, it can be made possible tosatisfy a request for an excellent sliding property with the use of asingle member, although in the past, a plurality of kinds of members arecombined so as to achieve an improvement in the sliding property whilesupplementing their individual properties with each other. Accordingly,a reduction in the cost of materials can be made due to a reduction inthe number of component members required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the construction of a sealingdevice according to a first embodiment.

FIG. 2 is a schematic cross sectional view showing a mounted state ofthe sealing device.

FIG. 3 is a schematic diagram showing part of an outer peripheralsurface of the seal ring in an enlarged scale.

FIG. 4 is a schematic cross sectional view of concave portions.

FIG. 5 is a schematic cross sectional view showing a sealing deviceaccording to a second embodiment.

FIG. 6 is a schematic diagram showing the schematic construction of atesting device.

FIG. 7 is a chart showing a comparison between average values of thesliding resistances of seal rings.

FIG. 8 is a chart showing a comparison between end-point temperatures.

FIG. 9 is a chart showing a comparison between amounts of leakage.

FIG. 10 is a chart showing a comparison between amounts of sliding heatgenerated and sliding resistances.

FIG. 11 is a chart showing a comparison between the sliding resistances.

FIG. 12 is a schematic cross sectional view of a sealing deviceaccording to the prior art.

FIG. 13 is a schematic cross sectional view of irregularities formed bymeans of shot processing.

EXPLANATIONS OF REFERENCE NUMERALS

-   1 Sealing device-   2 Seal ring-   20 Outer peripheral surface-   21 Side surface-   22 Concave portions-   23 Convex portions-   23 a Initial sliding surface-   3 Elastic ring-   4 Housing-   40 Inner peripheral surface-   5 Shaft-   50 Annular groove-   51 Side surface-   52 Groove bottom-   6 Annular gap

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, the best mode for carrying out the present inventionwill be described in detail by the way of example based on the followingembodiments while referring to the accompanying drawings. However, it isto be understood that the measurements, materials, shapes, relativearrangements and the like of component parts described in theembodiments should not be construed as limiting the scope of the presentinvention in any manner, in particular unless specified otherwise.

First Embodiment

A sealing device according to a first embodiment of the presentinvention will be described while referring to FIG. 1 and FIG. 2. FIG. 1is a schematic diagram showing the construction of the sealing deviceaccording to this embodiment, wherein FIG. 1A shows an appearancethereof as seen in an axial direction, and FIG. 1B is an arrow view asseen from arrow A of FIG. 1A, showing a partial cross section thereof.FIG. 2 is a schematic half cross sectional view showing a mounted stateof the sealing device according to this embodiment, wherein FIG. 2Ashows a state with no pressure applied, and FIG. 2B shows a state withpressure applied.

The sealing device 1 according to this embodiment is used, for example,as a sealing device for a piston in a hydraulic cylinder, i.e., aso-called piston seal that is fitted into an annular groove formed on anouter peripheral surface of the piston for sealing an annular clearanceor gap between the piston and the cylinder.

The sealing device 1 is comprised of a seal ring 2 and an elastic ring3, and is fitted into an annular groove 50 formed on an outer peripheralsurface of a shaft 5 so as to seal an annular clearance or gap 6 betweena housing (cylinder) 4 with a shaft hole and the shaft (a piston, a rod,or the like) 5 inserted into the shaft hole.

The seal ring 2 is an annular member of a substantially rectangularcross section, and it is arranged at an opening side of the annulargroove 50. An outer peripheral surface 20 of the seal ring 2 is placedin sliding contact with an inner peripheral surface 40 of the housing 4to form a sealing surface with respect to the housing 4. In addition,upon application of oil hydraulic pressure OF, the seal ring 2 is pushedto a side opposite to a fluid to be sealed (non-hydraulic pressure side)(A) of the annular groove 50, whereby a side surface (end face) 21 ofthe seal ring 2 at the side opposite to the fluid to be sealed (A) isplaced into intimate contact with a side surface 51 of the annulargroove 50, thereby forming a sealing surface with respect to the shaft5.

As materials for the seal ring 2, there can be usedpolytetrafluoroethylene (PTFE), which is generally used widely as asliding material, and in addition thereto, the entire general-purposethermoplastic resins such as polyamide (PA), polyether-ether-ketone(PEEK), polyphenylene sulfide (PPS), polyacetal (POM), and so on, canalso be used. In particular, polyamide, being excellent in pressureresisting property and yet low in cost, can provide the seal ring withthe function of a back-up ring when used for a high pressure piston sealcomprising four component members, so the number of component partsrequired can be reduced due to abolition of a backup ring, thus makingit possible to achieve further cost reduction. In addition, for example,a polyamide resin with glass fiber mixed therein may be used, and inthis case, the amount of glass fiber mixed or filled is 20-40 percent byweight, and preferably, 25-35 percent by weight. Also, other additivessuch as molybdenum disulfide can be used as required.

The elastic ring 3 is an annular member of a substantially circularcross section made of a rubber material such as nitrile rubber (NBR),polyurethane (PU), etc., and it is fitted under compression into betweenthe seal ring 2 and a groove bottom 52 of the annular groove 50. Theelastic ring 3 serves to urge the seal ring 2 toward the housing 4 sideunder the action of its elastic restoring force, so that the contactbetween the seal ring 2 and the housing 4 can be increased. Here, it isto be noted that the cross-sectional shape of the elastic ring 3 is notlimited to the circle, but instead, a variety of kinds of shapes suchas, for example, a rectangular cross section, etc., can be adopted asrequired.

The seal ring 2 has a plurality of concave portions 22 formed on itsouter peripheral surface 20, which is a sliding surface thereof withrespect to the inner peripheral surface 40 of the housing 4. The concaveportions 22 are recesses (holes) which are minute with respect to thearea of the outer peripheral surface 20, and are formed uniformly overthe entire surface of the outer peripheral surface 20.

In a sealing device having a sliding sealing surface such as the sealingdevice 1 according to this embodiment, it is designed, for example, suchthat a part of the fluid to be sealed such as hydraulic operating oil orthe like in the hydraulic cylinder can leak into between the innerperipheral surface 40 of the housing 4 and the outer peripheral surface20 of the seal ring 2 within a range in which no substantial influencewill be exerted on the operation, the sealing performance and the likeof related equipment, whereby it is constructed such that lubricatingfilms (oil films) of the fluid to be sealed are formed on slidingsurfaces so as to reduce the wear and the sliding resistance of thesliding surfaces and so on.

The lubricating films formed of the fluid to be sealed, which isinterposed between the sliding surfaces of the housing 4 and the sealring 2, might become uneven or might not be formed with a sufficientthickness in the initial stage of use because the fluid to be sealeddoes not spread over the entire sliding surfaces, or the lubricatingfilms, even if once formed evenly or sufficiently, might be reduced inthickness or might disappear (cause oil film shortage) because the fluidto be sealed does not stay on the sliding surfaces but gradually moves(leaks out) up to the non fluid-to-be-sealed side (A) by repeatedsliding movements. When such a state occurs, wear might be caused on theinner peripheral surface 40 of the housing 4 or the outer peripheralsurface 20 of the seal ring 2, and the sliding resistance of the slidingsurfaces might become large, as a result of which unusual noise,stick-slip, heat generation, etc., might be generated.

In this embodiment, it is constructed such that the concave portions 22formed on the outer peripheral surface 20 of the seal ring 2 function asoil sump holes, and hence lubricating films are liable to be formed, andat the same time, the thickness of the lubricating films are maintainedin a stable manner for a long period of time. That is, the fluid to besealed having leaked from the fluid-to-be-sealed side (O) to the slidingsurfaces accumulates in the concave portions 22, so the thickness of thelubricating films is maintained by the fluid to be sealed which has thusbeen accumulated in the concave portions 22, thereby suppressing thegeneration of oil film shortage.

In addition, the concave portions 22 also function as pressure chambersbetween themselves and the inner peripheral surface 40 of the housing 4.That is, the pressure in the chambers defined by the concave portions 22and the inner peripheral surface 40 of the housing 4 rises gradually dueto the gradual accumulation of the fluid to be sealed in the concaveportions 22, whereby there is generated a force that acts in a directionto separate the outer peripheral surface 20 of the seal ring 2 and theinner peripheral surface 40 of the housing 4 from each other. As aresult, an expansion force acting on the seal ring 2 and a contactpressure acting against the inner peripheral surface 40 of the housing 4can be reduced, thus making it possible to decrease the slidingresistance of the seal ring 2. In addition, in an annular oil groove asshown in the above-mentioned fourth technical document (FIG. 12), thevolume or storage capacity of the oil groove is large and an accordinglylong accumulation time is required, so it is not possible to increasethe pressure therein in an early time, and hence, an accumulation ofpressure can not be built up in an early stage of time, but in contrastto this, the concave portions as in the present application are so smallin volume, that the accumulation of pressure can be achieved in an earlytime.

Moreover, the plurality of concave portions 22, being minute incomparison with the area of the outer peripheral surface 20 of the sealring 2, are formed in a uniform manner over the entire surface of theouter peripheral surface 20, so even if a scratch or flaw or the likefor placing adjacent ones of the concave portions 22 in communicationwith each other is made on the outer peripheral surface 20, a situationwill be hard to occur that places the fluid-to-be-sealed side (O) andthe non fluid-to-be-sealed side (A) in communication with each other.

Further, by the provision of the plurality of concave portions 22, itbecomes possible to form the oil films in an efficient manner even whenthe stroke of the relative axial motion of the housing 4 and the shaft 5is short. That is, the fluid to be sealed that forms the lubricatingfilms is once held or retained in one of the concave portions 22 nearthe region-to-be-sealed side (O) with a first stroke of the shaft orpiston, and is then moved to the next one of the concave portions 22adjacent to the opposed region-to-be-sealed side (A) with a secondstroke of the shaft. By repeating this, the lubricating films can bespread on the whole area of the outer peripheral surface 20.

In addition, it is preferable to form the concave portions 22 by meansof laser irradiation. This will be described below in detail whilereferring to FIG. 3 and FIG. 4. FIG. 3 is a schematic diagram that showspart of the outer peripheral surface of the seal ring 2 in an enlargedscale, wherein FIG. 3A shows a state in which convex portions 23 areformed, and FIG. 3B shows a state in which the convex portions 23 havebeen worn out. FIG. 4 is a schematic diagram that shows the crosssection of the concave portions 22, wherein FIG. 4A is an AA section ofFIG. 3A, showing a state in which the convex portions 23 are formed, andFIG. 4B is a BB section of FIG. 3B, showing a state in which the convexportions 23 have been worn out.

As shown in FIG. 3A and FIG. 4A, by irradiating laser to the outerperipheral surface 20 of the seal ring 2 made of a thermoplastic resin,the concave portions 22 are formed and at the same time the materialmelted by the irradiation heat of the laser rises around the openingedges of the individual concave portions 22 to form the convex portions23 in such a manner as to enclose surroundings of the opening portionsof the individual concave portions 22.

As shown in FIG. 4A, such concave and convex shapes formed by the laserirradiation are not pointed ones like concave and convex shapes formedby means of shot processing, but instead, the convex portions 23 eachhave an outer peripheral surface 20 formed to gently rise with a tip endthereof being formed into a flat face. This flat surface functions as aninitial sliding surface 23 a. That is, at the time of starting of theequipment such as the hydraulic cylinder or the like (operation initialstage), the initial sliding surfaces 23 a of the convex portions 23become in sliding contact mainly with the inner peripheral surface 40 ofthe housing 4.

At this time, in spaces 23 b between individual convex portions 23, theouter peripheral surface 20 is in a state in which it is basically innon-contact with the inner peripheral surface 40 of the housing 4, so aclearance or gap is formed between the outer peripheral surface 20 andthe inner peripheral surface 40 of the housing 4. The clearance or gapformed between the outer peripheral surface of the seal ring 2 and theinner peripheral surface 40 of the housing 4 in spaces 23 b betweenthese individual convex portions 23 serves as a guide passage forguiding the fluid to be sealed to the sliding surfaces, so that thefluid to be sealed is made to easily spread over the entire slidingsurfaces.

In addition, the individual convex portions 23 are made intosubstantially collapsed shapes by being compressed at the time ofpressure application thereto or by being worn in the initial stage, andhence the gaps formed between the individual convex portions 23 becomein a substantially disappeared state. Also, it is constructed such thatat the time before being worn out, the individual convex portions 23 arereturned to their original state by elastic restoration when thepressure applied thereto is released, so gaps are formed again betweenthe individual convex portions 23. This operation operates in such amanner that the fluid to be sealed is inhaled into the gaps between theindividual convex portions 23 as if it breathes (pumping operation), andit is repeated until the convex portions 23 have been worn out.

As shown in FIG. 3B and FIG. 4B, when the convex portions 23 are wornout to disappear in accordance with the sliding movement thereof withrespect to the inner peripheral surface 40 of the housing 4, thesurroundings of the opening edges of the concave portions 22 in whichthe convex portions 23 are formed are finally made flush with the outerperipheral surface 20. At this time, a lubricating film of a sufficientthickness is formed over the entire outer peripheral surface 20 by meansof the guide passage formed between the individual convex portions 23,and at the same time, the fluid to be sealed is accumulated in theindividual concave portions 22 to a satisfactory extent.

Thus, at the time of starting, only the initial sliding surfaces 23 a ofthe convex portions 23 basically slide with respect to the innerperipheral surface 40 of the housing 4, so the sliding area becomesmall, as a result of which the sliding resistance in the initial stage,in which the lubricating film has not yet been formed over the entiresliding surface to a satisfactory extent, can be reduced. Accordingly,the generation of stick slip, which is generally liable to occur at thestart of operation in which a stable lubricating film has not yet beenformed on the sliding surface can be suppressed.

Moreover, since it is constructed such that the fluid to be sealed canbe easily introduced into the sliding surfaces in a positive manner inthe initial stage, it is possible to obtain a satisfactory sliding(lubrication) characteristic in a relatively early stage of time. Thatis, the fluid to be sealed can be filled into the concave portions 22 atan early time, and at the same time, stable and good lubricating filmscan be formed at an early time.

Here, note that if laser processing is employed as a method of formingthe concave portions 22, they can be easily formed though other methodssuch as one using shaping dies, shot processing, etc., may be used aslong as concave and convex shapes as referred to above can be formed.

Regarding the size or dimensions of the convex portions 23, if toolarge, they might form a flow passage that acts to place thefluid-to-be-sealed side (O) and the non fluid-to-be-sealed side (A) incommunication with each other, thus resulting in leakage, so it isnecessary to design the size in a manner such that the convex portionsare substantially collapsed when pushed against the inner peripheralsurface 40 of the housing 4 under the application of pressure.

Here, it is to be noted that such concave portions and convex portionscan be easily formed because the base polymer of the seal ring made of aresin material is a thermoplastic resin. However, in case where the basepolymer is a thermosetting resin such as, for example, phenol or thelike, a material containing the base polymer is vaporized, without beingmelted, by the heat of the laser, as a consequence of which the concaveportions can be formed but the convex portions are not formed around theconcave portions, so it is impossible to obtain the improvement effectof the lubrication property in the initial stage.

Further, the individual concave portions 22 are uniformly formed asminute oil sump holes on the entire surface of the outer peripheralsurface 20 of the seal ring 2, and as specific dimensional shapesthereof, it is preferred that, for example, with respect to the sealring 2 having an outer diameter D of 100 mm and an axial width W of 6.96mm, each of the concave portions 22 take a substantially conical shapehaving a circumferential width L1 and an axial width L2 both in therange of 100-1,000 μm, and a depth in the range of 50-200 μm. Inaddition, it is also preferred that the individual adjacent concaveportions 22 be arranged apart from one another at a circumferentialinterval I1 and at an axial interval I2 both in the range of 100-300 μm.

As a specific method of producing the concave portions 22, the entirecircumference of the seal ring is processed by irradiating laser withina circumferential range of about 20 mm in a pulsed manner whilesupporting the seal ring of the above-mentioned dimensions in arotatable manner, and by rotating the seal ring a constant angle perirradiation in a repeated manner. It is verified that by setting a spotsystem for scanning lines to be about 300 μm, there were formed concaveportions each having a circumferential width L1 of 346 μm, an axialwidth L2 of 497 μm, and a depth of 116 μm. In addition, thecircumferential interval I1 and the axial intervals I2 of each concaveportion at this time are 200 μm and 135 μm, respectively, and the heightof each convex portion is about 10-20 μm.

Here, note that in the above explanation, a use example has beendescribed in which counterpart members (housing and shaft), on which asealing device is mounted, relatively move in an axial direction, and aseal ring slides in the axial direction, but the condition of use inwhich this embodiment can be applied is not limited to this. That is,this embodiment can be used even in a use condition in which counterpartmembers relatively rotate with respect to each other and a seal ringslides in a circumferential direction, and in this case, the sameeffects as those described above can be achieved.

Although in the above explanation, reference has been made to the casewhere a sealing device is fitted in an annular groove formed on an outerperipheral surface of a shaft, the present invention is not limited tothis but may be constructed such that a sealing device is fitted into anannular groove formed on an inner peripheral surface of a shaft hole ina housing, and an inner peripheral surface of a seal ring is in slidingcontact with an outer peripheral surface of the shaft.

Second Embodiment

A sealing device according to a second embodiment of the presentinvention will be described while referring to FIG. 5. FIG. 5 is aschematic cross sectional view showing the sealing device 1′ accordingto the second embodiment. Here, note that constructions common to thoseof the first embodiment are identified by the same symbols and anexplanation thereof is omitted. Constructions, their operational effectsand the like not particularly described are similar to those in thefirst embodiment.

The outer peripheral surface 20 of the seal ring 2 has axially oppositesides thereof formed into taper surfaces 24, respectively. With this,the sliding area with respect to the inner peripheral surface 40 of thehousing 4 becomes small, and the sliding resistance thereof can bereduced. In addition, the contact pressure of the outer peripheralsurface 20 with respect to the inner peripheral surface 40 of thehousing 4 can be reduced by a wedge effect that is produced by the fluidto be sealed entering a clearance or gap of a substantially wedge-shapedcross section formed between the taper surfaces 24 and the innerperipheral surface 40, and at the same time, there can be obtained aneffect that the fluid to be sealed is positively introduced into thesliding surfaces.

(Verification of a Lubrication Improvement Effect)

Next, the improvement effect of the lubrication property by means of theconcave portions 22 will be verified based on the test results obtainedby a comparison with a prior art article while referring to FIG. 6through FIG. 11. FIG. 6 is a schematic diagram showing the schematicconstruction of a testing device. FIG. 7 is a chart showing a comparisonbetween average values of the sliding resistances of seal rings with andwithout concave portions. FIG. 8 is a chart in which a comparison ismade between end-point temperatures according to the presence or absenceof the concave portions. FIG. 9 is a chart in which a comparison is madebetween amounts of leakage according to the presence or absence of theconcave portions, wherein FIG. 9A shows an amount of leakage in theprior art article, and FIG. 9B shows an amount of leakage in an articleof an embodiment of the present invention, respectively, these figuresbeing the measurement results with more large number of samples. FIG. 10is a chart in which a comparison is made between the generation ofsliding heat and the sliding resistance according to the presence orabsence of the concave portions, wherein FIG. 10A shows end-pointtemperatures, and FIG. 10B shows the sliding resistances, respectively.FIG. 11 is a chart in which a comparison is made between the slidingresistances according to the difference in the cross-sectional shape.

As shown in FIG. 6, the testing device is provided with a cylinder 4 a,and a piston 5 a that is connected with an unillustrated drivingcylinder and is constructed to make a stroke in the interior of thecylinder 4 a in an axial direction, wherein sealing devices 2 a and 2 bin the form of evaluation samples are fitted into annular grooves formedon an outer peripheral surface of the piston 5 a at its opposite ends,respectively. In addition, it is further constructed such that a wearring 7 is fitted on the piston between the two samples, and pressure isapplied between the two samples while passing through the interior ofthe piston 5 a by way of a hose 8. A reference numeral 9 denotes a loadcell, and a reference numeral 10 denotes a wall temperature measurementpart that measures the wall temperature of the cylinder 4 a.

A constant pressure of 10 MPa is applied between the two samples, andthe piston 5 a is caused to stroke by means of the driving cylinder,with the sealing devices 2 a, 2 b being acted by the pressure, wherebythe sealing devices 2 a, 2 b are driven to slide with respect to theinner peripheral surface of the cylinder 4 a. The speed of the stroke isset to 50 mm/sec, and the length of the stroke is set to 100 mm.

The wall temperature of the cylinder 4 a is caused to rise by thegeneration of heat due to the stroke of the piston 5 a, and thetemperature at the time when the rising of the wall temperature has beensaturated is assumed to be an end-point temperature. In addition, theload that is required for the stroke when the end-point temperature hasbeen reached is measured by the load cell 9, and the starting oractuation resistance and the sliding resistance are gathered from thewaveform of the load thus measured.

A sealing device according to the above-mentioned first embodiment,i.e., one having a plurality of concave portions formed on an outerperipheral surface (sliding surface) of a seal ring, was used as anembodiment or inventive article, and a seal ring having no concaveportion formed thereon according to the prior art was used as a priorart article, wherein comparisons were made among a variety of kinds ofvalues such as end-point temperatures, sliding resistances, etc.

As shown in FIG. 7, with respect to the average value of the slidingresistances, the prior art article without concave portions changes at avalue of about 750 kgf or less, whereas the inventive article with theconcave portions changes in a range of about 400-450 kgf. That is, it isfound that with respect to the average value of the sliding resistances,the inventive article is reduced by about 40 percent of the prior artarticle.

As shown in FIG. 8, with respect to the end-point temperatures, theprior art article without concave portions is 90 degrees Celsius,whereas the inventive article with the concave portions is 80 degreesCelsius. Thus, the inventive article is lower by 10 degrees Celsius thanthe prior art article. That is, it is found that the inventive articleis less prone to be influenced by the generation of heat due to slidingmovements as compared with the prior art article.

As shown in FIG. 9, substantially no leakage occurred in either of theprior art article and the inventive article, and hence, the provision ofthe concave portions resulted in no increase in the amount of leakage.That is, it is found that the presence or absence of the concaveportions does not influence the sealing property or performance of theseal ring.

As shown in FIG. 10, the generation of sliding heat in the inventivearticle is decreased by 16 degrees Celsius at 10 MPa, and by 28 degreesCelsius at 30 MPa, with respect to the prior art article. In addition,the starting or actuation resistance (the maximum value of the slidingresistance when the seal ring begins to slide) is reduced by about 100kgf, and the difference between the starting resistance and the slidingresistance (the sliding resistance during sliding movement afteractuation) and the sliding resistance change are also reduced,respectively. That is, it is found that the sliding property at the timeof actuation (starting) has been improved, and at the same time, thesliding property thereafter (after the starting period has elapsed) hasalso been improved. In addition, it is found that a heat generationreducing effect becomes greater in accordance with increasing pressurein use.

In FIG. 11, the changes in the sliding resistance (Fr) according to thedifference in the shape of the sliding surface (the outer peripheralsurface of the seal ring) are shown. Here, one having no concave portionformed on its sliding surface is used as a prior art article 1, andanother one having an annular groove formed on its sliding surface, forexample, as in the prior art example shown in FIG. 12, is used as aprior art article 2, whereas a further one having a plurality of minuteconcave portions formed uniformly over the whole of its sliding surfaceas in the above-mentioned first embodiment is used as an inventivearticle, and these articles are respectively compared with one another.

As shown in FIG. 11, the prior art article 2 having the annular grooveformed on the sliding surface is reduced in either of the actuationresistance, the difference between the starting resistance and thesliding resistance, and the change of the sliding resistance, withrespect to the prior art article 1 having the flat sliding surface.However, the inventive article having minute concave portions formed inplurality and uniformly over the whole of the sliding surface is furtherreduced in either of these values with respect to the prior art article2. That is, it is found that a sliding property improving effect isgreater, in the case of the uniform formation of a multitude of minuteconcave portions on the whole of its sliding surface as in theembodiments of the present invention, than in the case of the formationof a single, or a small number of, relatively large groove-likeregion(s) as in the prior art example shown in FIG. 12.

The invention claimed is:
 1. A sealing device which is fitted into anannular groove formed in one of a housing with a shaft hole and a shaftinserted into said shaft hole and serves to seal an annular gap betweenthese two members, and which includes a seal ring made of a resin thatis in sliding contact with the other of said two members, and an elasticring that is fitted between said seal ring and said annular groove,wherein: said seal ring has a plurality of concave portions formed onits sliding surface which is in sliding contact with the said othermember; and said seal ring has convex portions which are formed so as toenclose said concave portions, respectively, and which rise from saidsliding surface and at the same time have initial sliding surfaces,respectively, said sliding surface between said convex portions beingrelatively higher than said concave portions, said concave portionsbeing formed as separate laterally and circumferentially spaced concavefeatures.
 2. The sealing device as set forth in claim 1, wherein saidconcave portions are formed by irradiating laser to said slidingsurface, and said convex portions are formed by a material which ismelted by the irradiation of the laser to rise around opening portionsof said concave portions, respectively.
 3. The sealing device as setforth in claim 1, wherein, said seal ring is made of a resin material ofwhich a base polymer is thermoplastic resin.
 4. A method for producing asealing device which is fitted into an annular groove formed in one of ahousing with a shaft hole and a shaft inserted into said shaft hole andserves to seal an annular gap between these two members, and whichincludes a seal ring made of a resin that is in sliding contact with theother of said two members, and an elastic ring that is fitted betweensaid seal ring and said annular groove, wherein said seal ring has aplurality of concave portions formed on its sliding surface which is insliding contact with the said other member, and said seal ring hasconvex portions which are formed so as to enclose said concave portions,respectively, and which rise from said sliding surface and at the sametime have initial sliding surfaces, respectively, comprising: formingsaid concave portions by irradiating laser to said sliding surface, saidconcave portions being formed as separate laterally andcircumferentially spaced concave features; and forming said convexportions by rising of a material around opening portions of said concaveportions, respectively, which is melted by the irradiation of the laser.5. The method for producing the sealing device as set forth in claim 4,wherein, said seal ring is made of a resin material of which a basepolymer is a thermoplastic resin.